Present methods of determining the location of front-line friendly units, command posts and mobile forces are inaccurate to the point of inhibiting the efficient employment of both air and ground support. The time-consuming procedure of map reference and visual sighting is a manual task which is mangified by the inadequate methods of exchanging such information among all elements of a landing force. Consequently, there must be established an integrated sub-system structure of position location and navigation equipment which will derive and disseminate timely, automated and up-dated information.
A concept of operation is herein proposed which provides self-contained, readily-portable equipment capable of transmitting range pulses in the UHF band and relaying the range data of additional transmitters that may be assigned to other operational forces. A synchronized time-zero and a slot-time-reporting sequence permits master installations to receive and record all such emitted pulses and to position-fix the location of all units of the system with a high degree of accuracy by means of trilateration. The digital-data-transmission capability of the system can provide navigational guidance for amphibious and wheeled vehicles as well as for helicopters and fixed-wing aircraft. Through the exchange of target information between units, control over the firing of artillery and missiles may be achieved. To accomplish these objectives, the invention provides for the establishment of primary master and sub-master stations which will receive, process and optionally display the signals received from all of the ranging units in a visual presentation identifying and locating such units with geographical precision.
A feature of the present concept resides in its ability to overcome the line-of-sight attenuation problem by providing alternate routes for range and data transmission. This results from the capability of each ranging unit employed in a given operational situation to relay to the master station range data respecting all other units in its vicinity.
It is a further feature of the present concept that each "user" within a military force (or spatial region) is capable of transmitting its own ranging pulse and data block, ranging on other units, and relaying the memorized range and data block of such other stations or units on a time-ordered basis within an assigned time slot. The basic equipment for accomplishing this objective consists of a clock module, a ranging data transmitter, a data control logic module, a ranging data receiver, and a data relay transmitter. The ranging equipment automatically computes the range to a transmitting unit from the beginning of the unit time slot until the time of receipt of the signal. All units are "counting in time" with each other synchronously and transmitting within an assigned time slot automatically. Each receiving unit computes the range to the transmitting unit and stores the computed range data in a memory unit until the completion of that unit's ranging cycle. A relaying sequence then commences which permits each unit to relay the computed range information in a time-ordered sequence to the master station on an assigned frequency. The transfer of data by direct transmission or alternate path relay overcomes the limitations of terrain obstacles to UHF transmissions without the requirement for an airborne relay capability.
The remainder of the disclosed system consists of one or more master stations each of which includes a clock module, a ranging data transmitter, a ranging data receiver, a re-synchronization logic module, a control logic module, an antenna and a relay data receiver. The master station receives the ranges and data block information from the ranging units either directly (if line-of-sight transmission permits) or indirectly through the relay capability of the ranging units. A computer assimilates the ranging information, and, by trilateration (that is--by ascertaining the size and shape of a triangle by measuring each of its three sides), determines the relative position of all using units. The relative position of the using units thus computed can readily be converted into a geographic coordinate system by determining the orientation of the entire set of measured triangles with respect to any known reference, such, for example, as a north asimuth determined by a gyro-compass.
It will now be recognized that a principal objective of the present concept is to provide a highly accurate ranging method and apparatus capable of providing continuous location data on a plurality of stations or units the individual positions of some or all of which may be undergoing constant change. The invention herein discloses is particularly applicable to situations where presently-known equipment is either inoperative or insufficiently accurate, or where the size and weight of the necessary apparatus precludes its use. The system of the present disclosure is designed to supplement or replace the use of radar, IFF, beacons and tactical data systems employing automatic communication links to process position information after it has been collected by radar or voice reporting. The simplicity and reliability of the present apparatus also renders it particularly suitable for employment as a collision-avoidance system for both military and commercial aircraft.